1. Field of the Invention
The present invention relates to a projection system, and more particularly, to a single panel illumination system and projection display apparatus using the same, by which color purity is enhanced.
2. Discussion of the Related Art
Recently, a display device has a tendency for developing into its lightweight, slim size and wide screen, and more particularly, its lightweight and slim size become a matter of concern.
To achieve the light weight and slim size, a projection display instrument needs to employ a single panel illumination system using one display panel instead of a 3- or 2-panels illumination system using three display panels.
The single panel illumination system enables low price, lightweight and slim size which are smaller than those of the 3-panels illumination system. Yet, the single panel illumination system implements separation/synthesis of the three primary colors, red, blue and green of light by color sequential driving, thereby having radiation intensity lower than that of the 3-panels illumination system.
To supplement such a disadvantage of the single panel illumination system, color scrolling methods of implementing color by illuminating at least two kinds of color on a display panel instantly have been devised.
FIGS. 1 to 4 are configurational diagrams of illumination systems of a single panel projection display device using a rotating prism, color wheel or color drum according to a related art. And, FIG. 5 and FIG. 6 are diagrams for representing color variations of illuminating light on a single display panel of the projection display device according to a time, in which a color scrolling method of implementing three colors on the panel instantly is exemplarily shown.
FIG. 1 is a configurational diagram of an illumination system of a single panel projection display device using three rotating prisms.
Referring to FIG. 1, a reference number 101 indicates a light source and reference numbers 102 and 103 indicate fly eye lenses, respectively. Reference numbers 106, 108, 115 and 118 indicate first to fourth dichroic mirrors transmitting or reflecting light of a specific wavelength band, respectively. Reference numbers 110 and 112 are total reflection mirrors of reflecting incident light unconditionally, respectively. And, reference numbers 113, 114 and 109 are first to third rotating prisms diverting a light path according to a rotating angle, respectively. In this case, the first dichroic mirror 106 has a red light reflection characteristic and a green and blue light transmission characteristic by dichroic coating. The second dichroic mirror 108 has a green light reflection characteristic and a blue light transmission characteristic by dichroic coating. The third dichroic mirror 115 has a green light reflection characteristic and a red light transmission characteristic by dichroic coating. And, the fourth dichroic mirror 118 has a red and green light reflection characteristic and a blue light transmission characteristic by dichroic coating.
Namely, white light projected from the light source 101 is split into cell units by a first fly eye lens (FEL) 102 and a second fly eye lens (FEL) 103 to be condensed on a specific portion of a PBS array 104. The PBS array 104 splits incident light into linearly polarized lights having an optical axis each, and more particularly, into an S-wave and a P-wave to project the S-wave to a condensing lens 105. In doing so, the P-wave is converted to an S-wave by a ½λ plate (not shown in the drawing) partially attached to a backside of the PBS array 104 and is then projected on the condensing lens 105. The condensing lens 105 condenses the light projected from the PBS array 104 and then projects the condensed light to the first dichroic mirror 106. The dichroic mirror is operative in splitting incident light by reflection/transmission according to a wavelength band. For instance, the first dichroic mirror 106 reflects red light of the incident light but transmits green light and blue light.
The red light reflected on the first dichroic mirror 106 proceeds to the total reflection mirror 112 via another condensing lens 111. The total reflection mirror 112 totally reflects the incident red light to the first rotating prism 113 as it is.
And, the green and blue lights transmitted through the first dichroic mirror 106 proceed to the second dichroic mirror 108 via another condensing lens 107. The second dichroic mirror 108 reflects the incident green light and transmits the incident blue light. The green light reflected on the second dichroic mirror 108 proceeds to the second rotating prism 114 and the transmitted blue light proceeds to the third rotating prism 109.
Each of the first to third rotating prisms 113, 114 and 109 has a rectangular shape. And, the first to third rotating prisms 113, 114 and 109 are situated on light paths of the R, G and B lights, respectively. The first to third rotating prisms 113, 114 and 109 change proceeding directions of the R, G and B lights according to their rotating angles, respectively. In other words, the first to third rotating prisms 113, 114 and 109 are independently turned to change imaging positions of the R, G and B lights imaged on a display panel (e.g., LCD or DMD) 121 according to their rotating angles, respectively and scroll the imaging positions of the lights of here color sequentially.
The red light having been transmitted through the first rotating prism 113 is transmitted through the third dichroic mirror 115 to proceed to the fourth dichroic mirror 118, while the green light having been transmitted through the second rotating prism 114 is reflected on the third dichroic mirror 115 to proceed to the fourth dichroic mirror 118. Moreover, the blue light having been transmitted through the third rotating prism 109 proceeds to the fourth dichroic mirror 118.
The fourth dichroic mirror 118 reflects the red and green lights and transmits the blue light to be projected on the PBS 120 via the condensing lens 119. The PBS 120 transmits the incident R, G and B lights so that the transmitted lights can proceed to the display panel 121.
In doing so, since the initially set rotating angles of the first to third rotating prisms 113, 114 and 109 are different from each other, the R, G and B lights are imaged on different portions of the display panel 121, respectively to be scrolled in a predetermined direction according to being driven. As the imaging positions are scrolled fast, the display panel 121 scrolls R, G and B signals according to the incident R. G and B lights. Hence, 3-color light signal is sequentially implemented on each pixel of the display panel 121. And, the implemented 3-color light signal is integrated by time to display a color image. The image implemented on the display panel 121 is enlarged to be projected on a screen via the PBS 120 and a projection lens (not shown in the drawing).
A process of scrolling an R/G/B color bar by rotations of the first to third rotating prisms 114, 114 and 109 is shown in FIG. 5, in which a color bar provided to a surface of the display panel 121 is periodically moving when the synchronized prisms corresponding to the respective colors are rotated. For instance, if the R/G/B color bar is formed on the display panel 121, a color image of one frame is formed when the R/G/B color bar, as shown in FIG. 5, is circulated once.
FIG. 2 is a configurational diagram of an illumination system of a single panel projection display device using a color wheel, in which reference numbers 201, 202 and 203 indicate a light source, an integrator and a color wheel, respectively.
White light projected from the light source 201 is homogenized in the integrator and polarized light converter 202 to be converted to a linearly polarized light having one optical axis to proceed to the color wheel 203.
Color pieces of the color wheel 203 rotate centering on an axis of the color wheel 203 to cut off the polarized incident light sequentially. After having passed through the color wheel 203, the incident light is sequentially changed into lights of R, G and B colors. Namely, the color wheel 203, which consists of a series of the color pieces of R, G and B transmission filters, is rotated by such a driving means as a motor to split the incident light into R, G and B colors on a time basis and then scrolls the respective split R, G and B colors sequentially to implement colors.
The light beam of which colors are split by the color wheel 230 is sequentially passed through an illumination lens array 204 and a PBS (polarizing beam splitter) 205 or TIR prism to proceed to a display panel 206. And, the display panel implements an image to correspond to the incident R, G and B lights. Namely, as the color wheel 203 is rotated, the R, G and B lights are sequentially scrolled on the display panel 206.
The image implemented on the display panel 206 is enlarged to be projected on a screen via the PBS or TIR (total internal reflection) prism 205 and a projection lens (not shown in the drawing). Hence, a viewer can recognize a synthesized color image that is formed by averaging a specific color projected on the screen according to a time basis.
A process that the R/G/B color bar is scrolled by the rotation of the color wheel 203 is shown in FIG. 6.
Referring to FIG. 6, if the R/G/B color bar is formed on the display panel 206, a color image of one frame is formed after completion of one circulation of the R/G/B color bar for example.
FIG. 3 shows an illumination system of a single panel projection display device using a color drum, in which reference numbers 300, 310 and 320 indicate a light source, a polarizing converting unit and a color drum, respectively.
Referring to FIG. 3, the polarizing converting unit 310 consists of a first FEL 311, a second FEL 312, an illumination lens array 314, and a TIR prism or total reflection mirror 315.
First of all, while light projected from the light source 300 is split into cell units by the first and second FELs 311 and 312 of the polarizing converting unit 310 to be condensed on a specific portion of the PBS array 313. The PBS array 313 polarizes the non-polarized white light in one direction (P- or S-wave direction) to be projected on the illumination lens array 314. The illumination lens array 314 condenses the light projected from the PBS array 313 to project to the TIR prism 315. The TIR prism 315 then diverts a proceeding path of the incident light by total reflection to make it pass through the color drum 320 which is rotating.
The color drum 320 is provided with a cylindrical transmission plate and dichroic coating is processed on the transmission plate to allow R, G or B light to be selectively transmitted. The color drum 320 is rotated at a predetermined speed by a rotational driving means such as a motor to split the incident light into R, G and B lights and to sequentially irradiate the split R, G and B lights on a display panel 370 via lens arrays 330, 340 and 350 and a PBS 360. Namely, the R, G and B lights are sequentially scrolled on the display panel 370 as the color drum 320 is rotated. An image implemented on the display panel 370 is enlarged to be projected on a screen via the PBS 360 and a projection lens.
FIG. 4 shows another example of an illumination system of a single panel projection display device using a color drum, in which reference numbers 401, 402 and 403 indicate a light source, a polarizing converting unit and a color drum, respectively. The polarizing converting unit 402 may consist of a PCCR (polarization converting and color recapturing) integrator.
Referring to FIG. 4, white light projected from the light source 401 is condensed on an aperture of the PCCR integrator of the polarizing converting unit 402. The condensed light is introduced into the integrator via the aperture and is then be split into P-wave and S-wave to maintain a polarizing direction of either the P- or S-wave through transmission and reflection. A light proceeding path of the one-directionally polarized light transmitted through the polarizing converting unit 402 is diverted by a TIR prism or total reflection mirror of a projection surface to pass through the color drum 403 that is rotating. A subsequent operation is the same of FIG. 3, of which detailed explanation is skipped.
Yet, in the single panel display devices shown in FIG. 1 to FIG. 4, at least two colors are simultaneously illuminated on one panel to implement colors. Hence, one color interferes with an area of another other color on the display panel to lower color purity.
For instance, blue and green lights intrude a red area to degrade red color purity. Likewise, a green or blue area is intruded by lights of the rest two colors to degrade its color purity. Such a color purity degradation always takes place in the color implementation system of the color scrolling method of implementing lights of at least two colors on one display panel simultaneously.
A process that 1-color light intrudes an area of another color is explained with reference to FIG. 7 as follows.
FIG. 7 shows an example that green color intrudes red color in a color scrolling method of illuminating 2-color light on a panel at one arbitrary moment.
Referring to FIG. 7, white light projected from a light source 701 is homogenized and converted to a linearly polarized light having one optical axis by an integrator and polarizing converter 702 to proceed to a color separation unit 703. Any device operative in performing color separation by a color scrolling method can be used as the color separation unit 703. For instance, a color drum, a color wheel, a rotating prism or the like corresponds to the color separation unit 703. Namely, the color separation unit 703 splits the white light into lights of R, G and B areas. And, it is also assumed that the polarizing converter 202 converts the white light to a P-wave polarized light.
The R, G and B lights split by the color separation unit 703 are sequentially illuminated on a display panel 706 via an illumination lens array 704 and a PBS 705.
In FIG. 7 which shows an example of implementing an entire image by red color, an ON signal is applied to an area of the display panel having the red light illuminated thereon and an OFF signal is applied to an area of the panel having the green and blue lights applied thereto, in the color scrolling method. According to a time basis, the R, G and B lights, as shown in FIG. 5 and FIG. 6, then sequentially propagate. In doing so, the red light proceeds to a projection lens 707 via a PBS 705 only but the green and blue lights fail to proceed toward the projection lens 707.
Namely, as the P-polarized red light is illuminated on the ON area of the display panel only, a polarized direction of the red light is converted to an S-wave from a P-wave to reflect to the PBS 705.
It is assumed that the PBS 705 is coated with a polarizing film to reflect the S-wave thereon and to transmit the P-wave therethrough.
If so, the S-wave red light is reflected on the PBS 705 toward the projection lens 707. The projection lens 707 then enlarges and projects the red light reflected on the PBS 705 to a screen (not shown in the drawing).
Meanwhile, the P-polarized green and blue lights, which are illuminated on the OFF area of the display panel, are reflected toward the PBS 705 without changing their polarized direction. Namely, the green and blue lights maintaining the P-polarization to be reflected toward the PBS 705.
For convenience of explanation, the green light among the green and blue lights is explained in detail as follows.
First of all, the green light, which is reflected on the OFF area of the display panel 706 to the PBS 705 to be in the P-polarized state G_p, is transmitted through the PBS 705 to enter the illumination lens array 704 as it is.
In doing so, it may happen that a portion G_p of the green light, as shown in FIG. 7, is reflected on a random surface of the illumination lens array 704 to arrive at the red area of the display panel via the PBS 705. Since the panel signal of the red area is ‘ON’, the P-polarized green light G_p is converted to the green light G_s to be reflected to the PBS 705. Since the PBS is coated to reflect the S-polarized light, the S-polarized green light G_s is reflected on the PBS 705 to the projection lens 707. The projection lens 707 then enlarges to project the S-polarized green light to the red area of the screen.
Meanwhile, the blue light, on which the same process of the green light is carried out, is enlarged to be projected on the red area of the screen as well. However, in case of the related art single panel projection display device enabling color implementation by illuminating at least two kinds of lights on the display panel simultaneously, the above-explained color intrusion degrades the quality of color image.